Abstract
Purpose: :
The multifocal electroretinogram (mfERG) P1 implicit time (IT) delays observed in adult diabetes do not decrease normally with fast light adaptation, suggesting that they represent a form of retinal neuropathy (Bearse et al., ARVO 2008). This study examines whether similar abnormalities exist in adolescents with diabetes.
Methods: :
MfERGs were recorded from one eye of adolescent subjects without retinopathy aged 12.8 to 21.5 years. We studied 3 age-matched groups: 30 individuals with type 1 diabetes; 11 with type 2 diabetes; and 26 controls. Nine retinal regions were examined: the central 7.5 deg; 4 areas between 3.25-10.5 deg eccentricity; and 4 areas between 10.5-22.5 deg. Within each region, the mfERG kernel series was used to synthesize isolated flash responses evoked under 4 adaptation conditions: (1) no flashes in the 40 ms preceding the stimulus; (2) a flash 40 ms before the stimulus; (3) a flash 26.7 ms before; and (4) a flash 13.3 ms before. Responses evoked by the preceding flashes were removed. IT of each isolated adapted response was then measured. IT changes relative to condition 1 (no preceding flash) were also calculated. Measurements were converted to Z-scores based on the control data and Z-scores >= 2 were considered abnormal (P < 0.023). For each adaptation condition, an eye was categorized as abnormal if 2 or more of the 9 Z-scores were abnormal (P < 0.02).
Results: :
As in normal adults, the effect of fast light adaptation (proximity of a preceding flash) on the controls’ isolated responses was a decrease in IT. The results of the 3 subject groups largely overlapped, with no significant differences among their means. However, the frequencies of eye abnormalities differed. In the type 1 group, 20%, 17%, 13% and 7% of the eyes had abnormally delayed IT for conditions 1 through 4, respectively. Based on IT change, 10%, 17% and 7% of their eyes were abnormal for conditions 2 through 4, respectively. In the type 2 group, 9%, 9%, 0% and 36% of the eyes were abnormal based on IT for conditions 1 through 4, respectively. Based on IT change, 9%, 18% and 36% of their eyes were abnormal for conditions 2 through 4, respectively. Controls had frequencies of abnormality < 3%.
Conclusions: :
Whereas mfERG IT is delayed in many eyes of adolescents with type 1 diabetes, IT abnormalities decrease with higher light adaptation. In contrast, adaptation does not decrease IT normally in many eyes of adolescents with type 2 diabetes, indicating greater neuropathic changes. The results suggest that subclinical neuropathy occurs in the retinas of many adolescents with diabetes.
Keywords: electroretinography: clinical • diabetic retinopathy • diabetes